Some known measurement systems measure a conductivity of a specimen of interest by placing electrodes into contact with the specimen. A voltage is applied to the electrodes and a resulting current is measured. The conductivity is then computed from the measured current. In some cases, many electrodes are attached to the specimen so that a type of imaging is made possible, provided that conductivity varies spatially through the specimen. This latter condition is true for geological specimens and human tissue specimens.
An alternative is to generate eddy currents within the specimen through inductive coupling to an external coil. The eddy currents exist in proportion to the local conductivity of the material and can be detected in a number of ways. For example, an amount of electrical energy dissipated in the coil may be measured when the coil is placed near a specimen.
The eddy currents are typically generated using a probe or a sensor that oscillates in a resonance state. A phase-locked-loop (PLL) circuit may be included in the probe to automatically tune the probe such that the probe is maintained in the resonant state. In addition, such probes may require additional components to maintain the resonant state or to detect the energy dissipated, such as a peak detector and/or a variable resistor. The PLL circuitry and the additional components may undesirably increase a size and a cost of the probe.
Thus, there remains a need for systems and methods that non-invasively determine the conductance of an object in a cost-effective, accurate, and efficient manner.